Nutrition lactation R. G. - Postgraduate Medical Journal · pregnant or lactating mothersandthe extra0.5 mg/ day made by the National Research Council is largely arbitrary. Breast

Postgraduate Medical Journal (May 1979) 55, 303-310

Nutrition and lactation

R. G. WHITEHEADPh.D., M.A., F.I.Biol.

Medical Research Council Dunn Nutrition Unit, Milton Road, Cambridge CB1 4XJ

SummaryRecommended dietary allowances for women duringpregnancy are discussed in the light of actual intakesboth in the developing and industrialized countries.The difference between total energy intakes in theindustrialized countries (around 2900 kcal) and in thedeveloping countries (around 1600 kcal) is empha-sized. Data are provided from The Gambia whichdemonstrate the effect of seasonal changes in maternaldietary intake on the quantity of breast milk producedand on its quality. The relationship between breast-milk supply and infant growth is also demonstrated.

IntroductionProfessor Hytten (Hytten, 1979) has discussed the

relationship between maternal nutrition and the out-come of pregnancy. What he has said could beequally relevant to successful long-term lactation,because capacity for lactation may well be influencedby what the mother's diet has been during her preg-nancy, as well as whilst she has been nursing.Nutritionists, like paediatricians and gynaecologists,have come to recognize that healthy fetal and earlyinfant life are closely linked to the well-being of themother.

In this paper, however, the author will be con-centrating primarily on maternal dietary intakeduring lactation. Firstly he will review the extranutrient allowances that various expert committeeshave thought it advisable to recommend to cover theincreased demands of lactations. Then, he willconsider practical situations, both in the indus-trialized and developing countries, where mothersmay not be receiving these recommended levels, tosee what effect variations in dietary intake actuallyhave on the quality and quantity of milk produced.Human lactation is such a natural process that it hasnot really been subjected to the rigorous scientificstudy it deserves. It is hoped that the author of abook on the subject, recently published under thetitle The Tender Gift (Raphael, 1976), will not objectif it is here stated that her title illustrates a common

oversimplified approach which, for the uncritical,can lead to attitudes harmful to the young infant.Breast milk is not a gift: the nutrients contained inmilk do not materialize out of thin air. Eitherdirectly or indirectly they must come from themother's diet.Most expert committees have assumed that the

needs of an infant will be satisfied by a milk outputof 850 ml/day. In communities where lactation is anormal event lactation lasts for at least one year andTable 1 shows the average amounts of various

TABLE 1. Energy and nutrient content in one year's supplyof breast milk*

Energy 217,175 kcal Iron 240 mgProtein 3-3 kg Vitamin A 186 mgFat 13 kg Vitamin C 12 g.Carbohydrate 23 kg Riboflavin 95 mgCalcium 1-1 kg Folic acid 16 mg

* These data are based on the assumption that the milkyield is 850 ml/day and the milk has the composition describedin DHSS, 1977.

nutrients which would be contained in a typicalyear's supply - based on the latest analyses whichhave been carried out in milk from British mothers -(Department of Health and Social Security (DHSS),1977). Using energy as a baseline and assuming anefficiency of dietary energy conversion of 80%o, theaverage British mother would need to consume165 kg extra food to produce this amount of milk;in a typical developing country (The Gambia) itwould be 247 kg because of the low energy contentof the diet. In communities where food is in shortsupply it is not surprising that many women do notreceive anything like so much extra food.

Recommended dietary allowancesProtein and energy

Perhaps the most complete set of dietary recom-mendations for lactation are those in the American

0032-5473/79/0500-0303$02.00 © 1979 The Fellowship of Postgraduate Medicine

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R. G. Whitehead

National Research Council Recommended DietaryAllowances (National Research Council (NRC),1974) and these are summarized in Table 2.

TABLE 2. Extra daily nutrient allowances for lactation (NRC,1964)

Nutrient Non-lactating Lactating Increase

Energy (kcal) 2100 2600 500Protein (g) 46 66 20Retinol (jtg) 800 1200 400Vitamin D (,ug) 10 10 0Vitamin E (mg) 12 15 3Vitamin C (mg) 45 80 35Riboflavine (mg) 1 5 2-0 0.5Nicotinic acid (mg) 14 18 4Vitamin B6 (mg) 2.0 2.5 0.5Folate (,Lg) 400 600 200Thiamine (mg) 1.0 1.3 0.3Calcium (mg) 800 1200 400Iron (mg) 18 18 0Zinc (mg) 15 25 10

It is very difficult to define exactly how muchextra dietary energy is needed and any recommenda-tion can only be a rough guide. It is important to payadequate attention to individual circumstances. Onecomplicating factor is the amount of fat which hasbeen laid down during pregnancy. If this is little, thenmore dietary energy during lactation is needed, andvice versa. The amount of dietary energy requiredalso depends upon the work a woman does. In somesocieties pregnancy and nursing are not allowed tomake any difference and women continue with hardmanual work. In other countries women are pro-tected at this time and assume a more or lesssedentary existence, and thus do not need so muchextra energy. The extra protein allowance of 20 g/dayis based on the assumption that the milk contains1-2 g protein/100 ml and that dietary nitrogen isutilized with normal efficiency. There is also agenerous allowance for individual variation.

VitaminsBreast milk contains about 50 ,tg retinol/100 ml

and, on the assumption that the mother will secrete850 ml, an extra dietary allowance of around400 tg/day is made by most authorities for lactation.The reader will notice that no extra allowance hasbeen made to cover vitamin D. This does not mean,of course, that breast milk contains no vitamin D -

it does, in the water-soluble sulphate form - but it isalways difficult to define allowances for this vitaminbecause so much is synthetized via sunlight and theskin. The 10 ,tg is very much a token safety allowancefor the non-lactating as well as the lactating mother.The extra vitamin E allowance was fixed on thebasis of the concentration of cx-tocopherol in humanbreast milk.

Considerable extra allowances have also beenmade by the Americans for vitamin C duringlactation, to allow for the vitamin C content ofbreast milk. Most lactating women also secrete 0.3-0-5 mg riboflavin in their breast milk each day andthe extra 0.5 mg allowance is to cover this amount.

Allowances for nicotinic acid are somewhatarbitrary and emphasize another of the difficulties inestablishing needs for lactations. There is thepossibility, with a number of nutrients, that meta-bolic efficiency, in this case the conversion oftryptophan to nicotinic acid, may be greater whenneeds are greater. With nicotinic acid this increasedefficiency is by no means proved and most expertcommittees have assumed that extra vitamin allow-ances should be increased proportionately withenergy at these times, and that is the reason for theextra 4 mg. Likewise with vitamin B6, there is littleor no decisive information on the needs of eitherpregnant or lactating mothers and the extra 0.5 mg/day made by the National Research Council islargely arbitrary.

Breast milk contains about 50 ,tg of folate perlitre, and, assuming a 25%4 efficiency of digestion,absorption and conversion to milk folate, an extra200 ug/day is usually recommended for lactatingwomen. The thiamine increment is to cover the extradietary energy recommended for lactation. Thiamineis essential for the metabolism of carbohydrates.Breast milk does not contain large amounts ofvitamin B12 and the 3 hg/day allowed for non-pregnant women would probably sustain the mothersthrough lactation as well; but nevertheless an extraone jig has been allowed by the Americans, more asa token than anything else, for lactating women.

MineralsBreast milk contains considerable amounts of

calcium and the breast milk secreted each dayrepresents a net loss to the mother of some 250-300mg calcium. For this reason the NationalResearch Council have allowed-like FAO/WHO(1962)- an extra 400 mg. It must be remembered,however, that we are by no means sure of thecalcium requirements of non-pregnant women. Itappears that people who habitually live on lowcalcium intakes may utilize dietary calcium muchmore efficiently than, say, the average woman woulddo in the U.S.A.

Defining iron requirements for women on a publichealth basis is always difficult. The reader will notethat the NRC (1974) have made no extra allowanceto cover lactation. This is for 3 reasons: breast milkdoes not contain very much iron, amenorrhoea isusually a feature during lactation, and finallyAmerican allowances for non-pregnant women arealready high - many would say impracticably high;

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Nutrition and lactation

certainly they are more than the correspondingDHSS (1969) recommendations. It would be theopinion of many nutritionists that the most rationalprocedure is for the doctor to assess a mother's ironrequirements clinically on an individual basis and toprovide iron in medicinal form to those who prove tohave particularly high needs.

Considerably enhanced allowances are also recom-mended for zinc. Zinc is important for infant growth.As with calcium, however, it seems likely thatmaternal need and the efficiency of utilization willdepend greatly on the dietary level to which theindividual has become accustomed. This is particu-larly important when one considers the developingcountries; an uncritical extrapolation from U.S.A.recommendations may not always be fully justified.

The practical situationThese, then, are the theoretical extra require-

ments for lactation. In practice, many women comenowhere near receiving extra allowances of thismagnitude. What effect does this have on thequantity and quality of milk produced by the motherand on the growth and development of her offspring?

This is a question of importance not just to thedeveloping countries, but for the Western world aswell. In the industrialized countries too little atten-tion has been paid to whether or not the under-standable desire of a woman to regain her figurequickly might mean she eats too little, thus mini-mizing her ability to produce sufficient milk to meetthe increasing demands of her growing infant. In arecent survey commissioned by DHSS (Martin,1978), the main reason given for stopping it bywomen who had established successful lactation wasthat they had too little milk to satisfy an infant whosedemands were increasing with his size.

In a recent survey carried out for the Birds EyeAnnual Review (1978), on 'food myths', it emergedthat 85% dismissed the idea that pregnant andlactating women needed to 'eat for two'. The pub-licity 'blurb' that went out with this publication waswidely quoted, both in the press and on radio, andthe fact that this 'myth' was dismissed by 85% ofmothers was highlighted as one of the most en-couraging findings of the survey. Encouraging fromthe point of view of slimming maybe, but what aboutlactation? For poor people in the developing coun-tries the issue is more acute; adequate provision ofbreast milk is of life and death importance for themajority of infants. Yet it is known that manynursing mothers are receiving less than 50% of therecommended allowances for energy and mostnutrients. It is arguable that protein-energy malnu-trition in the young pre-school child in fact beginswith the under-feeding of the mother.

It is unfortunate, however, that so few quanti-

tative studies, either in the under-developed or theindustrialized countries, have been carried out wherebreast-milk output and quality have been directlycompared with maternal dietary intake; the evidencethat links diet to milk output is largely circum-stantial. In the United Kingdom, Thomson, Hyttenand Billewicz (1970) in Scotland, Naismith andRitchie (1975) in London, and Whichelow (1976) inCambridge have all shown that successfully lactatingwomen have much higher daily energy intakes thanbottle-feeding mothers (Table 3). But this does not

TABLE 3. Energy intakes (kcal/day) of mothers with breast-fed or bottle-fed infants

Breast-fed Bottle-fedmean (± s.e. mean)

Thomson et al. (1970) 2716 (107) 2125 (76)Naismith and Ritchie (1975) 2930 (106) 2070 (127)Whichelow (1976) 2728 1958

prove that dietary insufficiency is linked with theneed to bottle feed. In the developing countries totalenergy intakes of 1500-1800 kcal/day and 20-50 gprotein are commonplace. In all studies so far pub-lished, but unfortunately in different sets of women,mean breast-milk output is considerably lower thanthe 850 ml/day which forms the basis of most expertcommittee reasoning and the 720-760 ml/day whichwas the average output found in a recent study ofSwedish women (L6nnerdal, Forsum and Ham-braeus, 1976).

In The Gambia, as shown in Fig. 1 (Whitehead etal., 1978), there is a marked seasonal variation in thefood energy intake of lactating women. During therainy season the energy expenditure ofwomen is alsogreatly increased because of the high level of farmingactivities at this time. It is strongly suggestive fromthe present data that these 2 factors - heavy manualwork and reduced maternal food intake - are associ-ated not only with dramatic alterations in bodyweight but also with a reduced milk output. It hasalso been demonstrated that this reduced milk out-put is not primarily because of less frequent feeding,but because the amount of milk produced per feed isreduced. The author's provisional conclusion is thatthe actual capacity for milk production by thewomen is reduced. Simple regression analysisbetween food intake and milk output, however, doesnot produce a particularly high correlation. Pre-sumably, ifwe had had an accurate way of measuringthe routine energy expenditure of the women, thebalance between energy intake and energy outputwould produce better correlations.Only a few direct attempts have been made in the

developing countries to see whether or not maternaldietary supplementation can actually increase milk

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R. G. Whitehead

400

., 350o

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250'

2000

1800 o

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1400 a

1200

1000

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FIG. 1. Seasonal variations in food energy intake, body weight and milk out-put in rural Gambian women (Whitehead et al., 1978). A----A Energyintake; o--o maternal body weight; A-A milk output.

yield. In general it is fair to say the results from thesestudies have not been particularly inspiring. Theamount of extra milk produced has not beenstriking; although some improvement was usuallyevident, a poor lactator was rarely transformed into agood one. Outputs were still well below 850 ml/day.It must be pointed out, however, that the nature ofthe dietary supplementation has not always beenparticularly rational.Two early reports, by Adair (1925) and Kleiner,

Tritsch and Graves (1928), recorded only slightlyincreased volume in earlier lactation as a result ofsupplementation, but the supplements were largelycarbohydrate in nature. Deem (1931) investigated theeffect of supplementation using a variety of diets, butjust for a short time. Only a 10% increase in milkoutput was achieved, although this could have beendue to the short investigative period. In the Wuppertalstudy, carried out after World War II, Gunther andStanier (1951) actually observed lower breast milkoutputs in groups supplemented with fat or withprotein and carbohydrate. Here there seem to havebeen sample selection problems.

In the Belgian Congo, Holemans, Lambrechts andMartin (1954) investigated the milk yield of 27women who had been receiving 40 g of skimmed

milk/day for one year. This provided a useful proteinsupplement but not much dietary energy to supportits metabolism. The results are shown in Fig. 2.Although there was some improvement, the totalvolumes were still low; the beneficial effect wasreally only significant in early infancy.Gopalan (1958) also studied the effect of protein

supplementation by maintaining 6 women with 5- to13-month-old infants on diets containing 61, 99 and114 g of protein respectively for consecutive periodsof 10 days. The total energy content of these dietswas 2900 kcal. The test-weighed mean milk outputs,however, for each period were only 402, 512 and490 ml/day respectively. But the investigative periodof that study was rather short to be of significance.One of the best studies carried out is that of

Chavez, Martinez and Bourges (1975) in Mexico.This was a 2-year longitudinal study in a poor andinadequately nourished rural community. The dietof the mother was supplemented from the 45th dayof gestation until weaning, with an extra 300 kcal/day. During the first 6 months of lactation the meanvolume of milk secreted was 15%/higher than innon-supplemented mothers, but it was also foundthat the milk of the supplemented mothers was moredilute (Fig. 3) and thus the nutrient benefit to the

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Nutrition and lactation 307

600-

_500

0)~~~~~~~~~~~~~~1

o\

E 400 /

300200

200 2 4 6

Infant age (months)

FIG. 2. The effect of maternal dietary supplementationwith skimmed milk on breast milk output in Congolesewomen (Holemans et al., 1954). o----o Supplementedmothers; 0 0 non-supplemented mothers.

child was only minimal. The problem with this studycould have been that 300 kcal was insufficient toboost baseline intakes to a satisfactory level. No datawere provided on the home intakes of the mothers.There is another possible explanation: preliminary

_2

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o 7

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0 3 6 9 12 15 18

Infant age (months)

FIG. 3. Effect of maternal dietary supplementation onthe solid content of breast-milk of Mexican women(Chavez et al., 1975). O----o Supplemented mothers;*- - --- non-supplemented mothers.

data from The Gambia has revealed additionalinterrelationships (Paul, Muller and Whitehead,1979). Figure 4 shows the association betweenchanges in the subcutaneous fat of nursing mothersduring the second 6 weeks of lactation, and theirdietary intake. Average customary energy intakeswere considerably below the recommended value,but in spite of this many of the lactating women areactually laying down fat, and the higher their energyintake, the more subcutaneous fat they are storing.It is conventionally assumed that subcutaneous fatis lost during lactation, not gained. Thus, in theundernourished mother there could be competitionbetween the replenishment of maternal subcutaneous

8 0

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-2

1000 1500 2000 2500 3000

Energy intake (kcol/doy)

FIG. 4. Relationship between different dietary energy intakesand the triceps skin fold thickness of Gambian women (Paul,Muller and Whitehead, 1979). r=0-4414; n=20; P<005.

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308 R. G. Whitehead

fat stores and the production of milk. In suchcircumstances it would not be surprising if anyimproved yield of milk arising after dietarysupplementation were less than expected.

This last finding emphasizes that for successfullactation it is probably insufficient to supplementjust during lactation. More likely, what is requiredis a general improvement in the nutritional status ofwomen.

Diet and the nutritional quality of human milkLet us consider maternal diet and milk quality.

Is the latter, as many believe, sacrosanct? The quickanswer would appear to be no. In general, the totalenergy content of breast milk does tend to be lowerin the undernourished mother. Figure 5 shows pro-visional data covering the first year of lactation inThe Gambia. The data were obtained from milksamples collected at 2 different times: one, at thebeginning of the rains, and one, after a period of lowenergy intake and high energy expenditure at the endof the rains. The energy content was lower in thelatter samples.

80

5 6

6 5

E 700

7

uJ 60-t' 85

II II3 6 9 12

Age (months)

FIG. 5. Energy content of human milk at 2 differenttimes of the year from Gambian women. (U.K. datafrom DHSS, 1977). 0 0 Start of rains; *----e end ofrains; U.K. milk.

5-0-

5 5 6

4-0 -29

1w0O ' 7

0L

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2.0

3 6 9 12Age (months)

FIG. 6. Fat content of Gambian human milk. (U.K. datafrom DHSS, 1977). 0 0 Start of rains; *----o end ofrains; U.K. milk.

1'4

00

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3 6 9 12Age (months)

FIG. 7. Protein content of Gambian human milk. (U.K.data, from DHSS, 1977). o-o Start of rains; *----eend of rains; U.K. milk.

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Nutrition and lactation 309

The mean fat content in the milk of well nourishedsubjects is around 42 g/100 ml (DHSS, 1977); butreports of the fat content in human milk from anumber of developing countries have provided valuesconsiderably lower than this (Belavady and Gopalan,1959; Crawford, Laurence and Munhambo, 1977),values from New Guinea being particularly bad -around 2-5 g/100 ml (Bailey, 1965; Venkatachalam,1962). The author's own provisional data fromGambian mothers are shown in Fig. 6. After thestress of intensive agricultural work and generallypoor energy intakes during the rains, the fat contentwas especially low. This is the main reason for thelow energy content. The average carbohydratecontent in the milk of British women is 7-4 g/100 ml(DHSS, 1977) and most studies from undernourishedcommunities have failed to demonstrate any signifi-cant difference between the lactose content of wellnourished and under-nourished subjects. In The

Gambia the lactose concentration tends to be higherat the end of the rains, but only marginally so.

In the case of protein, the average concentrationin the milk of well nourished mothers is around1 2 g/100 ml. Malnutrition does not seem to affectthis value greatly, although the author's own pre-liminary data (Fig. 7) again suggest seasonal dif-ferences.The vitamin content of milk also seems to be

dependent on the nutritional status of the motherand Fig. 8 shows this relationship for nicotinic acid,ascorbic acid, thiamine, and riboflavine. These datacome from a study of Deodhar and Ramakrishnan(1960) in Baroda, India, but similar findings havealso been reported by other workers.

It can be said in conclusion that although there isstrong circumstantial evidence to suggest that thecapacity of the mother to produce sufficient amountsof breast milk of high nutritional quality is influenced

20-(a) (b)

125 30

10 200

5 30

0.21 0*36 0.58 1*23 0-15 0-23 0*28 0*41

Dietary intake (mg/day)

5(c) (d

150 ~~~~~~~~~~~~~~~~4

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2*I 3-1 4.5 7-3 0-6 2-4 4*8 8*5

Dietary Intake (mg/day)

FIG. 8. Vitamin contents of milk from Indian women at different levels of intake(Deodhar and Ramakrishnan, 1960). (a) Thiamine, (b) riboflavine, (c) nicotinicacid. (d) vitamin C.

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310 R. G. Wlhitehead

by her dietary status, more practically orientatedwork needs to be done before we can make un-reserved recommendations at the public healthplanning level. In the meantime, those directlyresponsible for the health and welfare of nursingmothers and their babies should be taking due noteof the possibility that maternal nutritional statuscould be an important factor influencing not only theoutcome of pregnancy but also the ability of themother for long-term successful lactation.

ReferencesADAIR, F.L. (1925) Influence of diet on lactation. American

Journal of Obstetrics and Gynecology, 9, 1.BAILEY, K.V. (1965) Quantity and composition of breastmilk

in some New Guinean populations. Journal of TropicalPediatrics, 11, 35.

BELAVADY, B. & GOPALAN, C. (1959) Chemical compositionof human milk in poor Indian women. Indian Journal ofMedical Research, 47, 234.

BIRDS EYE ANNUAL REvIEw (1978) What Every HousewifeKnows. Birds Eye Foods Ltd, Walton-on-Thames.

CHAVEZ, A., MARTINEZ, C. & BOURGES, H. (1975) Role oflactation in the nutrition of low socio-economic groups.Ecology of Food and Nutrition, 4, 159.

CRAWFORD, M.A., LAURENCE, B.M. & MUNHAMBO, A.E.(1977) Breast feeding and human milk composition.Lancet, i, 99.

DEEM, H.E. (1931) Observations on the milk of New Zealandwomen. I. The diurnal variation in the fat content ofhuman milk. Archives of Disease in Childhood, 6, 53.

DEODHAR, A.D. & RAMAKRISHNAN, C.V. (1960) Studies onhuman lactation. Relation between the dietary intake oflactating women and the chemical composition of milkwith regard to vitamin content. Journal of Tropical Pedi-atrics and Environmental Child Health, 6, 44.

DEPARTMENT OF HEALTH AND SOCIAL SECURITY (1969)Recommended Intakes ofNutrientsfor the United Kingdom.Report on Public Health and Medical Subjects, No. 120.H.M. Stationery Office, London.

DEPARTMENT OF HEALTH AND SOCIAL SECURITY (1977) TheComposition ofMature Human Milk. Report on Health andSocial Subjects, No. 12. H.M. Stationery Office, London.

FAO/WHO (1962) Report of a FAO/WHO Expert Com-mittee on Calcium Requirements. WHO Technical ReportSeries, 230, FAO, Rome.

GOPALAN, C. (1958) Studies on lactation in poor Indiancommunities. Journal of Tropical Pediatrics, 4, 87.

GUNTHER, M. & STANIER, J.E. (1951) The volume and com-position of human milk. In: Studies of Undernutrition,Wuppertal 1946-49. Medical Research Council SpecialReport Series No. 275, p. 379. H.M. Stationery Office,London.

HOLEMANS, K., LAMBRECHTS, A. & MARTIN, H. (1954) Etudequalitative et quantitative du lait des femmes indigenes duKwango (Congo belge). Revue medicale de Litge, 9, 714.

HYTTEN, F.E. (1979) Nutrition in pregnancy. PostgraduateMedical Journal, 55, 295.

KLEINER, I.S., TRITSCH, J.E. & GRAVES, L.G. (1928) Influenceof supplementary feeding of carbohydrates upon lactation.American Journal of Obstetrics and Gynecology, 15, 172.

LONNERDAL, B., FORSUM, E. & HAMBRAEUS, L. (1976) Alongitudinal study of the protein, nitrogen and lactosecontents of human milk from Swedish well nourishedmothers. American Journal of Clinical Nutrition, 29,1127.

MARTIN, J. (1978) Infant Feeding 1975: Attitudes and Practicein England and Wales. Office of Population Censuses andSurveys, Social Survey Division. H.M. Stationery Office,London.

NATIONAL RESEARCH COUNCIL (1974) Recommended DietaryAllowances, 8th edition. National Academy of Sciences,Washington D.C.

NAISMITH, D.J. & RITCHIE, C.D. (1975) The effect of breast-feeding and artificial feeding on body-weights, skinfoldmeasurements and food intakes of forty-two primiparouswomen. Proceedings of the Nutrition Society, 34, 116A.

PAUL, A., MULLER, E. & WHITEHEAD, R.G. (1979) Seasonalvariations in energy intake, body-weight and skin-foldthickness in pregnant and lactating women in ruralGambia. Proceedings of the Nutrition Society (in press).

RAPHAEL, D. (1976) The Tender Gift: Breastfeeding. SchockenBooks, New York.

THOMSON, A.M., HYTTEN, F.E. & BILLEWICZ, W.Z. (1970)The energy cost of human lactation. British Journal ofNutrition, 24, 565.

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WHICHELOW, M.J. (1976) Success and failure of breastfeeding in relation to energy intake. Proceedings of theNutrition Society, 35, 62A.

WHITEHEAD, R.G., ROWLAND, M.G.M., HUTTON. M.,PRENTICE, A.M., MULLER, E. & PAUL, A.A. (1978) Factorsinfluencing lactation performance in rural Gambianmothers. Lancet, ii, 178.

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